Driven by military and civilian applications, the demand of very high resolution mapping
and accurate monitoring has increased rapidly over the recent years. Nowadays, it is
possible to create 4D models involving time variations using multiple synthetic aperture
radar (SAR) images, combined with interferometric methods. SAR has evolved to satisfy
a variety of applications for civilian and military users, for example by supporting
catastrophe management, detection of geological changes, monitoring large construction
sites or mines. With the help of SAR data obtained from the TerraSAR-X satellite, infrastructural
monitoring is made possible from a distance. The benefit of this is that
potential collapse within mines or tunnels could be prevented. Concrete degradation that
could lead to building collapse, endangering people’s lives can also be identified before
any catastrophe has the chance to occur.
Currently, Tomographic SAR (TomoSAR) is the most advanced and competent interferometric
SAR (InSAR) method in the area of urban monitoring. TomoSAR makes
monitoring in 4D possible by creating the 3D position with the motion parameters.
This thesis applies a new TomoSAR technique and method, developed by ZHU and her
colleagues, 2012 [1], on a very high resolution (VHR) spotlight data stack in the area of
Berlin. The images were taken by the TerraSAR-X satellite (Germany) over a timeframe
of 3 years. The result is a 3D point cloud of the observed area, with the velocity of linear
motion and the amplitude of periodic motion.
The result of the work that forms the basis for this thesis, is the realization of high
deformation and motion in Berlin’s infrastructure, especially around Berlin’s main station,
on bridges (” Überflieger Brücke”) and railways - often up to 10mm.
Table of Contents
1 Introduction
1.1 Motivation: The 4th Dimension
1.2 Purpose and Structure
1.3 About TerraSAR-X
1.3.1 TerraSAR-X Scanning Modes
2 Theoretical Basics - SAR Principles
2.1 SAR Geometry
2.2 SAR Phase
2.3 SAR Properties
2.3.1 Layover
2.3.2 Chirp
2.3.3 Speckle
2.4 SAR Image Resolution
2.5 InSAR Basics
2.5.1 Interferometric Phase
2.5.2 InSAR Athmospheric Influences
2.5.3 InSAR Height Retrieval
2.6 Persistent Scatterer Interferometry (PSI)
2.7 SAR Tomography
3 TomoSAR
3.1 TomoSAR Processing Procedures
3.2 Pre-Processing
3.3 Processing
3.3.1 TomoSAR System Model
3.3.2 TomoSAR Algorithm
4 Application on Berlin Data Stack
4.1 Downsampling
4.2 Quality Measurements
4.3 Creating Pixel Pairs
4.4 Integration
4.5 Filter Residual Phase
4.6 Upsamling and Estimation
5 Results and Analysis
5.1 Deformations and Movements
5.1.1 Seasonal Movements
5.1.2 Linear Movements
5.2 Verification and Observation of the processed SAR Data Stack
5.2.1 TomoSAR Result Observation
5.2.2 Virtual Inspection of Observation
5.3 Inspected Targets
5.3.1 ”Uberflieger Br¨ ¨ ucke”
5.3.2 ”Berlin Hauptbahnhof”
6 Conclusion
Objectives & Topics
The primary objective of this bachelor thesis is to utilize Tomographic SAR (TomoSAR) techniques on high-resolution TerraSAR-X satellite data to monitor and analyze 4D ground and infrastructure movements in urban areas, specifically focusing on the city of Berlin.
- Application of advanced TomoSAR processing methods to extract 3D positions and motion parameters.
- Analysis of seasonal and linear movement patterns in urban infrastructure.
- Technical evaluation of TerraSAR-X data and its suitability for high-resolution urban monitoring.
- Integration of SAR-derived point clouds with existing 3D models for ground truth validation.
Excerpt from the Book
1.1 Motivation: The 4th Dimension
The Earth is constantly and continuously moving. In many countries around the world, the fast expansion of urban areas is related to the significant expansion of construction areas and infrastructure. The vast amount of buildings and their degradation by nature could lead to building collapse and affirms the need for dynamic models (4D) in a dynamic world. For instance some latest catastrophes like the collaps of the Cologne city archive in Germany 2009 (Fig. 1), and the ground displacement near Shanghai Tower in China (Fig. 2). With the establishment of very high resolution sensors, the remote sensing technology, for example Synthetic Aperture Radar (SAR), helps to monitor urban infrastructure movements to prevent collapses.
There are many ways to monitor the urban area, but in this case we use SAR, because of the numerous benefits. SAR is an active remote sensing technique, providing images by scanning the earth’s surface with electromagnetic waves (microwaves) thereby generating images covering a large area. Unlike optical or laser devices, SAR is almost operational in every weather condition, since atmospheric absorption is very little on microwave bands [5][6]. However, with the slanted imaging geometry, SAR faces the ”layover” problems in urban areas with buildings [7]. Layover results in a pixel in a SAR image containing both the information from the ground and the building facade. Fortunately, using the technique called SAR tomography (TomoSAR), these ambiguities can be solved [8].
Using differential Interferometry, even very little building and ground movements can be measured and monitored to prevent collapses or other fatal accidents. High resolution SAR data can be used to create 4D-Models of areas, a 3D-Model including the time-dimension, therefore monitoring areas and building movement with Persistant Scatterer Interferometry (PSI), a method invented in 2001 [9]. Since the PSI method expects that every pixel only has one dominant point, TomoSAR can solve multiple scatterers and the layover-effect, which makes it a better observation method for buildings. With TerraSAR-X having a resolution close to 1m x 1m [6] and with up to 1mio PS/km2, it enables new possibilites in the civilian and military uses of remote sensing. This thesis aims to experiment with and exploit the potential of very high resolution (VHR) SAR in urban areas with TomoSAR using TerraSAR-X high resolution spotlight data.
Summary of Chapters
1 Introduction: Provides an overview of the motivation for 4D urban modeling, the potential of SAR technology, and the structure of the thesis.
2 Theoretical Basics - SAR Principles: Explains the fundamental physical and mathematical concepts of Synthetic Aperture Radar, including geometry, phase, and interferometry.
3 TomoSAR: Details the Tomographic SAR processing chain, focusing on system models and specific algorithms like SVD-Wiener and SLIMMER.
4 Application on Berlin Data Stack: Describes the practical implementation of the workflow, including downsampling, quality measurement, and spatial filtering using Berlin as the test area.
5 Results and Analysis: Presents the findings regarding deformation and movements, featuring an analysis of the Berlin Hauptbahnhof and the "Uberflieger Brücke".
6 Conclusion: Summarizes the effectiveness of TomoSAR as a tool for urban deformation monitoring and provides final insights on its practical utility.
Keywords
Tomographic SAR, TerraSAR-X, 4D urban modeling, Interferometry, InSAR, PSI, deformation monitoring, infrastructure, Berlin, spotlight data, signal processing, elevation, movement analysis, remote sensing, satellite radar.
Frequently Asked Questions
What is the core focus of this bachelor thesis?
The work explores the application of Tomographic SAR (TomoSAR) for monitoring 4D movement and deformation of urban infrastructure using high-resolution data from the TerraSAR-X satellite.
What are the primary themes discussed in the research?
Key themes include the principles of SAR and Interferometry (InSAR), the development of 4D models, the technical challenges of urban monitoring, and practical deformation analysis of specific structures like bridges and train stations.
What is the main objective or research question?
The objective is to test and validate whether TomoSAR, utilizing VHR spotlight data, can successfully provide accurate, millimeter-level measurements of building and ground movements in an urban setting.
Which scientific methods are applied?
The study employs TomoSAR processing, specifically using SVD-Wiener filtering to handle multiple scatterers within resolution cells, and incorporates spatial difference algorithms to mitigate atmospheric phase screen (APS) effects.
What is covered in the main section of the document?
The main section covers the theoretical foundations of SAR, the processing workflow (downsampling, integration, filtering), and a detailed result analysis focused on the infrastructure in Berlin.
Which keywords best characterize this research?
Essential keywords include Tomographic SAR, TerraSAR-X, 4D modeling, InSAR, deformation monitoring, and urban infrastructure.
How is the "layover" effect addressed in this thesis?
The thesis utilizes TomoSAR, which decomposes the information within a single resolution cell into different elevations, effectively resolving the ambiguities that typically cause the layover effect in standard SAR imaging.
What specific movement patterns were observed in Berlin?
The research identified significant seasonal motion patterns in materials like steel and glass, particularly noticeable at the Berlin Hauptbahnhof and railway bridges, likely caused by thermal expansion.
Why is the SVD-Wiener filter used in the processing?
The SVD-Wiener filter is utilized because it is computationally efficient and provides a robust, linear method for estimating unknown parameters and the true elevation of shifting scatterers.
- Arbeit zitieren
- Clemence Chee (Autor:in), 2012, Tomographic SAR Reconstruction of a 4D City using TerraSAR-X data, München, GRIN Verlag, https://www.grin.com/document/208933
